Method of exhausting vacuum tubes



Feb. 4, 1930. o, w, PIK 1,746,164

METHOD OF EXHAUSTING VACUUM TUBES Filed Jan. 21. 1928 HEA77/V6 CURRENT-Inventor:

Otis W. Pike by MW His Attorney.

Patented Feb. 4, 1930 UNITED STATES PATENT OFFICE OTIS W. PIKE, OFSCHENECTADY, NEW YORK, ASSIGNOB TO GENERAL ELECTRIC' COMPANY,ACORPORATION OF NEW YORK 2 METHOD OF EXHAUSTING VACUUM TUBES Applicationfiled January 21, 1928. Serial No. 248,581.

' The present invention relates to electric discharge devices and moreparticularly to a method forexhau'sting such devices.

While heretofore various methods have been employed to heat theelectrodes of a discharge device during evacuation and thus causeremoval of occluded gases, none of the former methods have providedmeans whereby a circulating current of appreciably greater value thanthat encountered in the usual or normal operation of the tube might bepassed between the electrodes to heat the various parts of the tubeduring the evacuation process.

According to the present invention, I heat 1 the electrodes, leads andseals by a high frequency circulating current which has a wave length ofthe order of five meters and is substantially independent of the currentdue to electron emission from the cathode. At this short wave length theinterelectrode capacity permits the passage of a circulating currentbetween the electrodes which is at least twice the value of currentsnormally encountered in the operation of the discharge device. In thismanner the electrodes and especially the leading-in wires and seals maybe heated during the exhaust to temperatures far in excess of thetemperatures ordinarily encoun- 80 tered in the operation of thedischargedevice and as a result an unusually high degree of vacuum maybe initially secured in the discharge device and this degree of vacuummay be maintained even under severe con- 85 ditions of use, such, forinstance, as are obtained when using the tube at the shorter wavelengths.

In carrying the present invention into effect, I connect the tube to beevacuated to a diffusion or other suitable exhaust pump and at the sametime oscillate the tube by means of a short wave oscillatory circuit ofsuch type and adjustment that the high frequency currents will be muchlarger than those normally encountered in practice.

.electrode 3 and filamentary cathode 4. A

diffusion exhaust pump 5 is connected to receptacle 1 through a glasstube 6 which passes through the usual liquid air trap 7. A short wave,oscillating, resonant circuit is associated with the discharge deviceand comprises grid 3, anode 2, inductances 8, 9, an ammeter 10, andalarge condenser or capacity unit 11. Radio frequency chokes 12, 13, 14and 15 are inserted in the electrode leads. A source of comparativelylow voltage alternating current is connected to a transformer 16 whichsupplies heating current to cathode 4, while a voltage of 500 volts orgreater may be connected to the anode lead and ground. A grid leakresistor 17 connects the grid leading-in wire with the secondary windingof the transformer 16.

As thus arranged the oscillating circuit will be resonant at a frequencyof about 60,- 000 kilocycles and will carry a current of very low powerfactor; With the pump 5 in operation, the circulating current flowing inthe oscillatory circuit will vary from 5 amperes upwardly, depending onthe size of the discharge device employed. The interelectrode capacitypermits the use of circulating currents of the value and frequencyindicated although currents of similar value and having relatively lowfrequencies could not be employed at voltages which would not endangerthe tube.

The circulating current in the oscillatory circuit depends upon thecapacity between the grid and anode and the high frequency voltage andis substantially independent of filament emission. For example, thecirculating current may have a value of about 30 amperes while theelectron current at the same time might not-have a value greater thanone ampere. Variations in the filament emission above normal operatingvalue will not cause any appreciable change in the circulating currentin the oscillatory circuit. The use of this large'circulating currenteffectively removes all occluded gas from the various parts of the tubeand permits the establishment of a very high degree of vacuum.

d What I claim as new and desire to secure by Letters Patent of theUnited States, is,- 1. The method of exhausting an electric dischargedevice containing a pair of electrodes, which comprises connecting saidpair of electrodes in a circuit resonant at a certain frequency andsupplying current of that frequency to said circuit while the dischargedevice is connected to an evacuating 2. The method of exhausting anelectric discharge device comprising a grid, anode and a filamentaryelectrode adapted to be heated to incandescence, which comprisesenergizing the filament coupling the grid and anode together to form ahigh frequency oscillatory circuit and supplying current to saidcircuit, the value of said current being dependent upon the capacitybetween the grid and anode.

3. The method of exhausting an electric I discharge device comprising agrid, anode and the grid and anode, then causingan alternatin spacecurrent of high frequency to flow tween the grid and anode while thedevice is being evacuated thereby to heat the electrodes and remove theoccluded ases, 1

have hereunto set of January, 1928. OTIS W. PIKE.

a filamentary electrode adapted to be heated to incandescence,whichcomprises rendering the filament electronically active, couplingthe grid and anode together to form a high frequency oscillatorycircuitand supplying current to said circuit, the value of said current beingsubstantially independent of the electron current in the device,

4, The method of exhausting an electric discharge device comprising agrid, anode and a filamentary electrode adapted to be heated toincandescence, which comprises causing the filament to emit electrons,coupling the grid and'anode together to form a high frequencyoscillatory circuit and supplying current to said circuit, the value ofsaid current being substantially independent of the current inthe devicedue to filament emission but dependent upon the capacity between thegrid and anode.

5. In the art of exhausting an electric discharge device comprising agrid, anode and a filamentary electrodeadapted to be heated toincandescencefthe" method which consists in energizing the- -filament toproduce electrons for reducing the impedance between I

